Implementation of lipidomics in clinical routine: Can fluoride/citrate blood sampling tubes improve preanalytical stability?

The impact of preanalytical sample handling on lipid stability has been assessed in human plasma using targeted LC-MS/MS quantification of endocannabinoids, sphingolipids and LPA, complemented by non-targeted lipidomics screening with LC-QTOFMS. The study involved incubation of whole blood and plasma from healthy volunteers at room temperature or in ice water for time periods ranging from 20 min to 24 h. The impact of two different anticoagulants, K3EDTA and sodium fluoride/citrate, on lipid stability was evaluated. It was found that the concentrations determined for several endogenous lipids vary when whole blood and plasma samples are processed at room temperature, whereas the concentrations of most lipids were stable for 4 h in ice water. Surprisingly, the detected amounts of endocannabinoids 1- and 2-arachidonoyl glycerol and arachidonoyl ethanolamide increased markedly by 60, 95, and 30% in K3EDTA whole blood after storage in ice water for only 20 min. When using sodium fluoride/citrate blood collection tubes, the stability of several lipids, including that of the endocannabinoids, was improved. Accordingly, it is absolutely necessary to keep the blood sampling and plasma processing time below 1 h to avoid ex-vivo formation of endocannabinoids. It is worth mentioning that baseline lipid levels differ when using K3EDTA or sodium fluoride/citrate blood sampling tubes, which emphasizes the importance of traceability of reported plasma concentrations to the used anticoagulant.

The omega-3 lipid 17,18-EEQ sensitizes TRPV1 and TRPA1 in sensory neurons through the prostacyclin receptor (IP).

Oxidized lipids play an important role in pain processing by modulation of the activity of sensory neurons. However, the role of many signalling lipids that do not belong to the classical group of eicosanoids, especially of oxidized omega-3 lipids in pain processing is unclear. Here we investigated the role of the endogenously produced omega-3 lipids 17,18-EEQ and 19,20-EDP in modulating the activity of sensory neurons. We found that 17,18-EEQ but not 19,20-EDP can sensitize the transient receptor potential vanilloid 1 and ankyrin 1 ion channels (TRPV1 and TRPA1) in sensory neurons, which depends on activation of a Gs-coupled receptor and PKA activation. Screening of different Gs-coupled lipid receptor-deficient mice, identified the prostacyclin receptor IP as putative receptor for 17,18-EEQ. Since 17,18-EEQ is synthesized by the Cytochrome-P450-Epoxygenase CYP2J2, we established a cellular mass spectrometry-based screening assay to identify substances that can suppress 17,18-EEQ concentrations. Using this assay, we identify the antidepressant venlafaxine and the antihypertensive drug telmisartan as potent inhibitors of CYP2J2-dependent 17,18-EEQ synthesis. These findings identify 17,18-EEQ as first omega-3-derived lipid mediator that acts via the IP receptor and sensitizes the TRPV1 channel in sensory neurons. Moreover, the results give a mechanistic explanation for the antinociceptive effects of venlafaxine, which are still not well understood. Like telmisartan, venlafaxine may reduce neuronal activity by blocking CYP2J2 and 17,18-EEQ synthesis and by inhibiting the IP receptor-PKA-TRPV1 axis in sensory neurons.

The G2A Receptor Controls Polarization of Macrophage by Determining Their Localization Within the Inflamed Tissue.

Macrophages are highly versatile cells, which acquire, depending on their microenvironment, pro- (M1-like), or antiinflammatory (M2-like) phenotypes. Here, we studied the role of the G-protein coupled receptor G2A (GPR132), in chemotactic migration and polarization of macrophages, using the zymosan-model of acute inflammation. G2A-deficient mice showed a reduced zymosan-induced thermal hyperalgesia, which was reversed after macrophage depletion. Fittingly, the number of M1-like macrophages was reduced in the inflamed tissue in G2A-deficient mice. However, G2A activation was not sufficient to promote M1-polarization in bone marrow-derived macrophages. While the number of monocyte-derived macrophages in the inflamed paw was not altered, G2A-deficient mice had less macrophages in the direct vicinity of the origin of inflammation, an area marked by the presence of zymosan, neutrophil accumulation and proinflammatory cytokines. Fittingly neutrophil efferocytosis was decreased in G2A-deficient mice and several lipids, which are released by neutrophils and promote G2A-mediated chemotaxis, were increased in the inflamed tissue. Taken together, G2A is necessary to position macrophages in the proinflammatory microenvironment surrounding the center of inflammation. In absence of G2A the macrophages are localized in an antiinflammatory microenvironment and macrophage polarization is shifted toward M2-like macrophages.

Targeting CYP2J to reduce paclitaxel-induced peripheral neuropathic pain.

Chemotherapy-induced peripheral neuropathic pain (CIPNP) is a severe dose- and therapy-limiting side effect of widely used cytostatics that is particularly difficult to treat. Here, we report increased expression of the cytochrome-P450-epoxygenase CYP2J6 and increased concentrations of its linoleic acid metabolite 9,10-EpOME (9,10-epoxy-12Z-octadecenoic acid) in dorsal root ganglia (DRGs) of paclitaxel-treated mice as a model of CIPNP. The lipid sensitizes TRPV1 ion channels in primary sensory neurons and causes increased frequency of spontaneous excitatory postsynaptic currents in spinal cord nociceptive neurons, increased CGRP release from sciatic nerves and DRGs, and a reduction in mechanical and thermal pain hypersensitivity. In a drug repurposing screen targeting CYP2J2, the human ortholog of murine CYP2J6, we identified telmisartan, a widely used angiotensin II receptor antagonist, as a potent inhibitor. In a translational approach, administration of telmisartan reduces EpOME concentrations in DRGs and in plasma and reverses mechanical hypersensitivity in paclitaxel-treated mice. We therefore suggest inhibition of CYP2J isoforms with telmisartan as a treatment option for paclitaxel-induced neuropathic pain.